The present invention relates generally to synchronous machines such as synchronous motors and synchronous power generators, and more particularly to a synchronous machine where field and armature windings are positioned on a stator.
Synchronous motors are available in a variety of designs, such as the rotating-armature, rotating-field and inductor types. The rotating-armature type synchronous motors comprise a magnetic field pole provided on a stator, and an armature winding provided on a rotor. The rotating-field type synchronous motors comprise an armature winding provided on a stator, and a magnetic field pole provided on a rotor. The magnetic field pole in the rotating-field type synchronous motors is typically a permanent magnet positioned on the rotor, or a magnetic field winding that is excited by direct current. The inductor-type synchronous motors comprise a magnetic field pole and armature winding provided on a stator, and an inductor provided on a rotor and having gear-like teeth and slots.
Since the armature winding is provided on the stator as mentioned, the rotating-field type synchronous motors are substantially free from mechanical damages and breakage and permit easy insulation, so that they are widely used today as driving means for rotating the spindles of various machine tools.
However, such rotating-field type synchronous motors where the field pole is a permanent magnet positioned on the rotor are disadvantageous in that the permanent magnet itself is expensive and must be secured firmly enough to not accidentally detach from the rotor and also in that it is difficult to provide large capacity because the magnetic field produced is always constant. The rotating-field type synchronous motors where the field pole is a magnetic field winding provided on the rotor are also disadvantageous in that they essentially require slip rings and a rotary transformer in order to supply field current to the rotor.